RV-4 engine mount question

AX-O · #1 08-28-2018, 12:38 PM

All,
Looking for real data from someone that has converted an RV-4 long gear from conical mount to a Dynafocal mount.

Specifically, did the prop flange end up in the same place? meaning no cowl mods were done. The vertical and lateral offsets were the same.

In the process of this prop swap I am evaluating the possibility to swap out engine mounts. Thanks for any help you can provide.

FinnFlyer · #2 08-28-2018, 06:01 PM

Hi Axel.
Do you already have the Dynafocal engine mount? I'm asking because I have one and am about to chop it up to fit a Mazda rotary (Renesis). So it doesn't matter if I start with a conical or Dynafocal engine mount. However, no clue if I have the long gear. How can I find out?

Finn

Russ McCutcheon · #3 08-28-2018, 08:35 PM

I talked to AX-O today about this and could not give him an answer, however the gear legs have no impact on the position of the crank flange regardless the engine type the mount is made to fit or the length of the legs so anyone who changed from conical to dynafocal or vice versa regardless the gear legs, how did the crank flange match up, did the spinner end up in the same place, if not then how much did it change?

Zero4Zulu · #4 08-28-2018, 09:40 PM

Would measurements from the firewall to the Spinner bulk head answer the question? Maybe someone with a Dynafocal could measure this on thier RV4.

gmcjetpilot · #5 08-28-2018, 09:43 PM

Good move upgrading conical and go dynafocal, good .... I would only suggest conical if you had a wood fixed prop.
If you stick with conical get LORD mounts. They cost more but will be far superior to the original rubber bushing design.
The dynafocal will transmits so much less vibrations and sag less.

As far as engines I am 99% sure the conical vs dynafocal does not change the engine crank flange psition up/down, left right.

The big difference in the cowls was, LONG COWL for a fixed prop with prop extension (or HC-F2YC Hartzell CS extended hub).
The SHORT COWL is for a Compact hub Hartzell, which is now the standard.

Van I recall longer offers LONG COWLS...They are all the same length. Fixed pitch props still need a prop extension, but shorter,
to match the same dimension as a Hartzell Compact Hub CS Prop.

AX-O · #6 08-28-2018, 11:18 PM

Quote:

Originally Posted by FinnFlyer

Hi Axel.
Do you already have the Dynafocal engine mount? I'm asking because I have one and am about to chop it up to fit a Mazda rotary (Renesis). So it doesn't matter if I start with a conical or Dynafocal engine mount. However, no clue if I have the long gear. How can I find out?

Finn

I dont have one. I am still researching. May not go that route depending on the data collected. I dont know the diference in measurement.

Quote:

Originally Posted by Zero4Zulu

Would measurements from the firewall to the Spinner bulk head answer the question? Maybe someone with a Dynafocal could measure this on thier RV4.

Yes that would be the right way but my engine is out and gone for a few weeks.

Quote:

Originally Posted by gmcjetpilot

If you stick with conical get LORD mounts. .

I dont have a vans cowl, do have the lord mounts. My question was does the dynafocal engine mount place the prop flange in the same place as the conical mount (regardless of extesion). I know the engine type does not change the prop flange location but the way the engine and engine mount interface may end up puting the prop flange in a different place requiring cowl mods.

I do have a source of truth data saying that the change from a short gear/mount to long gear did not require cowl mods.

131RB · #7 08-29-2018, 03:39 AM

Axel,
I am not sure what might happen for your swap but I can tell you several years ago I converted a RV4 short gear to a long gear. Both Dynafocal.
Everything changed, some things you would expect some not. I had to completely redo the baffling and ended up purchasing a new cowl and spinner as the old cowl was so far off it wouldn't even begin to go back on, and in such bad shape it was easier to replace.
It could be easy then again it could be a giant can of worms.
Ryan

sblack · #8 08-29-2018, 08:00 AM

I have to ask, how do you swap out mounts without changing your crank case? I feel stupid asking the question, but you only said you are doing a prop swap.

Russ McCutcheon · #9 08-29-2018, 08:30 AM

Quote:

Originally Posted by sblack

I have to ask, how do you swap out mounts without changing your crank case? I feel stupid asking the question, but you only said you are doing a prop swap.

He is considering changing or modifying his crankcase while his engine is off.

Russ McCutcheon · #10 08-29-2018, 08:41 AM

Quote:

Originally Posted by 131RB

Axel,
I am not sure what might happen for your swap but I can tell you several years ago I converted a RV4 short gear to a long gear. Both Dynafocal.
Everything changed, some things you would expect some not. I had to completely redo the baffling and ended up purchasing a new cowl and spinner as the old cowl was so far off it wouldn't even begin to go back on, and in such bad shape it was easier to replace.
It could be easy then again it could be a giant can of worms.
Ryan

If they were both type one Dyna mounts and they both came off my fixture then the engine position would not have changed at all, that fixture has been a constant since the early 80s, probably about 1982. All we did for the long gear was re position the "Z" frame in the base of the mount fixture and the center two attach points moved almost one hole but the dyna ring never moved in relation to the fire wall. How old is your -4, there are a few very early ones out there that have home made mounts and a few that have mounts from a different vendor, the ones i've seen where very rough.